1. Field of the Invention
The present invention relates to a manufacturing method of a field emission cathode.
2. Description of the Related Art
The field emission cathode used as an electron-emitting element is roughly classified into the hot cathode type and the cold cathode type. Among these, the hot cathode type is used in the field represented by a vacuum tube. However, the integration of the hot cathode type is difficult because it needs to be heated. On the other hand, the cold cathode type, which needs not be heated, can be formed into a fine structure, and hence is expected to be applied to a flat panel display, a voltage amplifying element, a high-frequency amplifying element, and the like.
As the cold field emission cathode, for example, a field emission cathode experimentally manufactured on a silicon wafer by C. A. Spindt is known. The cold field emission cathode can be manufactured, for example, by a method shown in FIG. 2.
In the manufacturing method, as shown in FIG. 2(a), an insulating layer 12 made of a thermally oxidized film is first formed on an Si substrate 11, and then a gate electrode layer 13 made of Nb is formed on the insulating layer 12.
Next, as shown in FIG. 2(b), a resist 14 is applied on the gate electrode layer 13 and is developed after being exposed via a mask (not shown), so that an opening section 15 having a predetermined pattern is formed.
Next, as shown in FIG. 2(c), a gate hole 16 is formed in the gate electrode layer 13 by reactive ion etching (RIE) using SF6, or the like. Further, the insulating layer 12 is subsequently etched by buffer hydrofluoric acid (BHF), so that a hole 17 reaching the Si substrate 11 is formed.
Next, as shown in FIG. 2(d), a sacrificial layer 18 made of Al is formed on the gate electrode layer 13 by oblique vapor deposition. In the oblique vapor deposition which is used to avoid deposition of Al on the Si substrate 11 in the hole 17, Al is vapor-deposited at a shallow incident angle almost in parallel to the Si substrate 11 toward the central axis X of the gate hole 16 and the hole 17 which are formed perpendicularly to the Si substrate 11.
Next, as shown in FIG. 2(e), an emitter material 19 made of Mo is vapor-deposited from vertically above the Si substrate 11, so that a cone-shaped emitter electrode 20 is formed on the Si substrate 11 in the hole 17. Then, as shown in FIG. 2(f), the field emission cathode is completed by removing the emitter material 19 together with the sacrificial layer 18 on the gate electrode layer 13. Note that at this time, if Al is vapor-deposited on the Si substrate 11 in the hole 17, the emitter electrode 20 is also removed simultaneously with the emitter material 19 and the sacrificial layer 18.
The field emission cathode shown in FIG. 2(f) comprises the Si substrate 11, the insulating layer 12 provided on the Si substrate 11, the emitter electrode 20 provided on the Si substrate 11 in the hole 17 provided in the insulating layer 12, and the gate electrode layer 13 provided on the insulating layer 12. Further, the gate electrode layer 13 comprises the gate hole 16 corresponding to the hole 17.
Meanwhile, in the manufacturing method shown in FIG. 2, as described above, the sacrificial layer 18 made of Al needs to be formed by the oblique vapor deposition in order to avoid that the emitter electrode 20 is removed simultaneously with the emitter material 19 and the sacrificial layer 18. However, the oblique vapor deposition has a problem that the control of film quality is difficult.
Further, the manufacturing method shown in FIG. 2 has a problem that a fluorine compound, which is derived from SF6 used for the etching of the gate electrode layer 13 and which is derived from buffer hydrofluoric acid used for the etching of the insulating layer 12, is attached to the hole 17 so as to become a gas adsorption contaminant for the emitter electrode 20. When the gas adsorption contaminant is attached to the hole, the life of the field emission cathode is shortened.
In order to solve the problems of the manufacturing method shown in FIG. 2, a manufacturing method shown in FIG. 3 is proposed (see Japanese Patent Laid-Open No. 7-14504).
In the manufacturing method shown in FIG. 3, an insulating layer 22 made of SiO2, a gate electrode layer 23 made of Nb, and a sacrificial layer 24 made of Al are first formed on an Si substrate 21 in this order as shown in FIG. 3(a).
Next, as shown in FIG. 3(b), a resist layer 25 is applied on the sacrificial layer 24 and is developed after being exposed via a mask (not shown). Thereby, an opening section 26 having a predetermined pattern is formed.
Next, as shown in FIG. 3(c), etching using a gas cluster ion beam B is performed by using, as a mask, the resist layer 25 with the opening section 26 formed therein, until the surface of the Si substrate 21 is exposed. Thereby, a hole 27 of the insulating layer 22 and a gate hole 28 of the gate electrode layer 23 are formed so that the gate hole 28 corresponds to the hole 27. At this time, it is possible to prevent the over-etching when the resist layer 25 is made to remain on a peel layer 4 after completion of the etching.
Next, after the remaining resist layer 25 is removed, an emitter material 29 made of Mo is vapor-deposited from vertically above the Si substrate 21 as shown in FIG. 3(d). Thereby, a cone-shaped emitter electrode 30 is formed on the Si substrate 21 in the hole 27.
Then, as shown in FIG. 3(e), a field emission cathode is completed by removing the emitter material 29 together with the sacrificial layer 24 on the gate electrode layer 23.
The field emission cathode shown in FIG. 3(e) comprises the Si substrate 21, the insulating layer 22 provided on the Si substrate 21, the emitter electrode 30 provided on the Si substrate 21 in the hole 27 provided in the insulating layer 22, and the gate electrode layer 23 provided on the insulating layer 22. Further, the gate electrode layer 23 comprises the gate hole 26 corresponding to the hole 27.
According to the manufacturing method shown in FIG. 3, it is not necessary to form the sacrificial layer 24 by the oblique vapor deposition. Further, the etching of the insulating layer 22 and the gate electrode layer 23 is performed by using the gas cluster ion beam. Thus, the attachment of the fluorine compound to the hole 27 is prevented, and hence the shortening of the life of the field emission cathode due to the gas adsorption contaminant can be prevented.